The invention refers to a process for extraction of an ethanol from a solution thereof, according to the preamble of appended claim 1.
The separation of ethanol from a low-grade ethyl-alcohol solution is attractive for several reasons. First, the ethanol, for example bio-ethanol, can to advantage be produced by biochemical processes, such as fermentation of a mixture of water and sugars (or from starches or ligno-cellulosic feedstock). By fermentation of the mixture, a mash is produced, comprising i.a. a solution, having a relatively low concentration of ethyl-alcohol (in general 5%-12%). Usually, bio-ethanol is obtained by a fermentation of a C-6 sugar/water solution having a low concentration (10-25%). By extracting high-grade alcohol from the low-grade solution, a useful product is obtained, which can be used i.a. as fuel. Moreover, the liquid mixture or solution from which the ethanol is extracted sometimes represents a co-product, the usefulness and market value of which is improved by said extraction of alcohol.
One problem is however the costs for the extraction of high-grade ethanol from such low-grade solutions.
Another problem is that one or more properties of the liquid, from which the ethanol is extracted, are affected in a negative sense, by usual present extraction processes, in which the liquid is heated and alcohol is extracted by distillation up to, e.g. 96% (azeotropic bio-ethanol). Further processing to produce net bio-ethanol 100% can be performed by the use of molecular sieves.